1. Field of the Invention
The present invention relates to a nitride-based semiconductor device, and particularly to a lateral power FET (FET: Field-Effect Transistor) used for controlling electric power.
2. Description of the Related Art
A circuit, such as a switching power supply or inverter, employs a power semiconductor device, such as a switching device or diode. The power semiconductor device needs to have a high breakdown voltage and low ON-resistance. The relationship between the breakdown voltage and ON-resistance includes a tradeoff relationship determined by the device material. Progress in technical development so far has allowed the power semiconductor device to have a low ON-resistance close to the limit determined by silicon, which is the main device material. Accordingly, it is necessary to change the device material, if a lower ON-resistance is required.
In recent years, attention is being given to research on a power semiconductor device using a wide band-gap semiconductor. For example, it has been proposed to use a wide band-gap semiconductor, such as a nitride-based material (e.g., GaN, AlGaN) or a silicon carbide-based material (SiC), as a switching device material, in place of silicon. The use of such a semiconductor can improve the ON-resistance/breakdown voltage tradeoff relationship determined by the device material, thereby remarkably reducing the ON-resistance. For example, HFET (HFET: Hetero-FET) having a hetero-structure formed by a GaN channel layer and an AlGaN barrier layer can realize a power FET with a high breakdown voltage/low ON-resistance.
Brief explanation will be given of the following publications listed as related arts.
[Patent publication 1] Jpn. Pat. Appln. KOKAI Publication No. 2002-184972
[Patent publication 2] Jpn. Pat. Appln. KOKAI Publication No. 2002-289837
[Patent publication 3] Jpn. Pat. Appln. KOKAI Publication No. 2001-284576
[Patent publication 4] Jpn. Pat. Appln. KOKAI Publication No. 11-145157
[Patent publication 5] Jpn. Pat. Appln. KOKAI Publication No. 07-135220
[Patent publication 6] Jpn. Pat. Appln. KOKAI Publication No. 2003-258005
[Patent publication 7] U.S. Pat. No. 6,534,801
[Patent publication 8] U.S. Pat. No. 6,690,042
[Patent publication 9] U.S. Pat. No. 6,586,781
[Patent publication 10] U.S. Pat. No. 6,548,333
The patent publications 1 and 7 disclose a HEMT (HEMT: High Electron Mobility Transistor) having an AlGaN channel layer, GaN buffer layer, and n-type GaN source/drain layer. The patent publication 3 discloses a HEMT having an AlGaN electron supply layer, and GaN electron accumulation layer. The patent publication 6 discloses a HEMT using an AlGaN/GaN hetero-junction.
The patent publication 2 discloses an FET having an AlGaN electron supply layer, GaN buffer layer, and n-type GaN source/drain layer. The patent publications 8 to 10 disclose a HFET having AlGaN/GaN junction layers to generate two dimensional electron gas.
The patent publication 4 discloses a GaAs-based FET having an embedded region to improve the breakdown voltage between the gate and drain. The patent publication 5 discloses a GaAs-based FET having a trench formed in the drain region and an electrode disposed in the trench to improve the breakdown voltage of the drain region.